Development of eyeglass-type display apparatuses in which a compact display apparatus embedded in an eyeglasses frame projects an image into the user's field of vision is progressing (for example, see patent literature PTL 1 to 3). For example, in the eyeglass-type display apparatus disclosed in PTL 1, an eyepiece for projecting an image is provided on the lower rim of an eyeglasses frame, and the user can observe an image only when looking at the eyepiece. The eyeglass-type display apparatus does not require a complicated wearing mechanism and can be worn on the user's head in the same way as regular eyeglasses.
For the eyeglass-type display apparatus to project an image onto the user's eyeball, a compact image display unit that does not block the user's peripheral vision is used, unlike a helmet-type or goggle-type head-mounted display device. When using such a compact image display unit, the area in which the user can see the image well (eye box) inevitably decreases. In a typical eyeglass-type display apparatus, the image therefore becomes harder to see if the position of the eyeglasses shifts even just a few millimeters. On the other hand, users exhibit individual variation in head size, position and shape of the nose and ears, and the like. Therefore, an adjustment mechanism for precise alignment (position adjustment) is necessary in an eyeglass-type image display apparatus so that, in accordance with individual differences, the position of the user's eye falls within the area in which the image can be seen.
For example, in the eyeglass-type image display apparatus disclosed in PTL 2, the front portion of the eyeglasses frame where the display is provided (eyeglass-front) is configured to allow rotational adjustment about an axis of rotation at the eyeball center as viewed from the side and allows the angle of incidence of the image to be adjusted with respect to the eyeball. In the eyeglass-type image display apparatus disclosed in PTL 3, a position adjuster is provided to allow the user to adjust the nose pads.